Following the quick technical development in the electronic industrial fields, various types of chips, such as the central processing unit (CPU), now have highly increased density of transistors provided thereon. While the currently available electronic devices have faster and faster data processing speed, they also consume more power and produce more heat during operation. The produced high amount of heat must be timely removed from the electronic devices, lest the raised temperature should cause burnout of the CPU and other electronic elements to adversely influence the whole system safety and performance. For the CPU to work stably, the electronic devices must be provided with better and more efficient heat dissipation devices to remove the heat produced by the CPU during operation thereof.
A conventional ring-type fan includes a frame and an impeller assembly. The frame has an air inlet and an air outlet, and a receiving space is defined in the frame between the air inlet and the air outlet. The frame also has a forward extended shaft seat located at a central area of the receiving space, and the impeller assembly is rotatably mounted in the receiving space and connected to the shaft seat.
The impeller assembly includes a hub, a plurality of impellers outward extended from and spaced around the hub, and a ring member connected to radially outer ends of the impellers. When the impeller assembly is mounted in the receiving space, a clearance is formed between the ring member and an inner wall surface of the frame. When the ring-type fan operates, external air flows into the receiving space via the air inlet and flows out of the frame via the air outlet. At this point, negative pressure will be produced at the air outlet, and part of the outflow of air forms backflows. The backflows pass through the clearance between the ring member and the frame to interfere with inflow of air and cause unsmooth flowing of outflow of air, resulting in lowered heat dissipation efficiency and performance of the ring-type fan and reduced service life thereof.
Accordingly, the prior art ring-type fan has the following disadvantages: (1) lowered heat dissipation efficiency; and (2) reduced fan performance.
It is therefore tried by the inventor to develop an improved impeller structure and ring-type fan using same, so as to overcome the problems in the prior art ring-type fan.